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THE 



CHEMISTRY OF MINERALTANNAGES 



WILLIAM M. NORRIS, 



PRINCETON, N. J. 




Cbr pvlrtc'on |lifss: 

C. S. KOBINSON & Co., Steam Puwek Pkinteus. 

ItitfS. 







Copyrit;lu, 1888, l>y Wm. M. Xorris, Princeton, N. J. 



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THE CHEMISTRY OF MINERAL TANNAGES 



During the last few years the manufacturers of morocco 
have made great changes in their output. There is little 
demand at present for the old styles of sumac tannages, 
" Brush Kid," " Pebbles," &c., but the newer styles of min- 
eral tannages with a glazed finish are largely (jailed for by 
shoe manufacturers, and gentlemen in the morocco trade are 
now striving to supply this demand. Although there are 
about as many different kinds of Glazed Kid on the mar- 
ket as there are manufacturers, still these may be grouped 
into five classes. 

1. Gambia and Alum Tannage. Many manufacturers 
are devoting their attention to this with success. The skins 
are placed in a vat, with a wheel, which contains the tan- 
ning liquor, where they are allowed to remain about two 
days. The tan varies in composition very much ; sonie 
use most all gambia with a little alum, while others use 
most all alum with a little gambia. The skins after being 
tanned are fat liquored, dried out, moistened, shaved, 
staked, blacked, and finished either dull or glazed. 

2. India Tanned Stock cleansed, retanned and finished 
into glazed kid ; this is largely turned out in the vicinity 
of Boston. 

3. Sumac Tauned Stock softened, staked, fat liquored 
and tiuished into dull and bright stock. This tannage has 
been brought to great perfection in Wilmington, Del. 



4 

4. Straight Alum Tannage which as turned out in this 
country is in many respects equal if not superior to the 
imported stock. 

5. Chromate Tannage, a beautiful new tannage very 
recently placed upon the market and in many respects 
superior to all. 

The last two are strictly mineral or chemical tannages, 
and while a knowledge of chemistry is not essential to suc- 
cess, still a correct understanding of the chemical properties 
and relations of the materials used, cannot fail to be of 
advantage and as I find that just such information is desired 
at present, I have prejjared this little pamphlet in which I 
have explained, as far as I am able, the chemistry of Min- 
eral Tannages and at the same time called attention to my 
prepai'ations which are exj^ressly manufactured for these 
tannages and which are now used by many of the leading 
manufacturers in the country. 

To describe these tannages in detail: — 

The skins are first soaked in large wooden tubs for 
three or four days until they are thoroughly and uniformly 
softened. They are then milled when they are ready for 
the 

LIME. 

Liming lasts about 10 days to two weeks. The skins 
are first placed in old limes for five days and then in a 
fresh lime, prepared by taking 1 lb. to every four skins, for 
about five days or until the hair yields readily to the pres- 
sure of the thumb. 

Lime is soluble in water at 60° Fah. only to the extent 
of 1 part in 778. It decreases in solubility at higher tem- 
peratures. At 212° Fah. (boiling), it takes 1270 parts of 



water to dissolve 1 part of lime. Owing thus to its limited 
solubility an excess of lime, if well slacked, is wasteful 
rather than injurious to the skins. 

The action of lime on skins is a solvent one ; the cells 
of the epidermis swell up and soften and the hair sheaths 
are loosened and dissolved. The fibres swell up and absorb 
water and become differentiated into finer fibrils so that 
the skin becomes plump ; in this manner bre^iking up 
the skin and exposing the fibrils and preparing it for 
the tan. It also acts upon the fat of the skins, convert- 
ing it more or less completely into an insoluble soap, and 
so hindering its injurious effects on the after tanning pro- 
cess and on the finished leathei'. If strong acid is used 
further on in the process for plumping the lime soap is 
decomjjosed and the grease again set free. 

Red Arsenic (Suphide of Arsenic), is frequently added 
to limes in which stock is placed to be finished into Glazed 
Kid. This if used in small quantities and judiciously is a 
good thing, — it hastens the unhairing and gives the grain a 
higher gloss. 

The various jireparations which are sold, and many of 
them patented, to unhair and to be added to limes almost 
all depend upon Sulphur in some form. 

These preparations merely render the lime more soluble 
and of course the time taken is lessened, but the lime pene- 
trates the skin io such an extent that in spite of frequent 
washings it remains there and causes much subsequent 
damage. 

It must be said, however, in this connection, that a 
small quantity of lime left in a skin is not considered by 
some injurious when the skin is subsequently tanned in 
alum, in fact it helps to set the alum in the skin in this 



6 

way. It combines with the sulphuric acid in the alum and 
forms Sulphate of Lime and Oxide of Alumina which is 
insoluble. Expressed in symbols the reaction is A1.^(S0J3 
+ 3CaO = A1,0, -f 3Ca SO,, but this sulphate of lime is 
undesirable to have in the skins. After liming the skins 
are uuhaired and then plar;ed in the 



" BATE." 
Dog pure is almost uuiversally used for this purpose, 
1 bushel to about 30 dozen skins. The skins after being 
unhaired and washed are thrown into an old bate where 
they are allowed to remain a few^ hours ; they are then re- 
moved and placed in a new bate where they remain over 
night. 

In this the skins completely lose their plumpness and 
become soft and slippery, the lime is largely neutralized 
and the dirt, grease and fine hairs work out of the skins 
freely when they are subsequently slated. The theory of 
the action of the bating process is somewhat obscure. 
Some attribute its action to the effects of the salts of 
ammonia, while no doubt the salts of ammonia do neut- 
ralize the lime, but when they are used alone they do not 
have the desired effect of softening the epidermis and pro- 
perly preparing the skins for the tan. In fact, as Proctor 
has pointed out, the process is a fermentive one. The 
active bate swarms with bacteria and to this fermentive 
or putrefactive action, rather than to its chemical constitu- 
ents the action of the bate must be attributed. 

That manufacturers should still continue to use this 
disgusting substance is extraordinary. This is no doubt 
due to the fact that the men in charge of this process of 
bating from long experience are perfectly familiar with the 
properties, action and effects upon skins of dog pure. And 
also to the fact that the various' substitutes introduced to 
the trade, owing to a misconception of their oi'iginators, as 
to what was required of a bate, did not accomplish what 
"vras desired. 

If the above theory is correct, a "Bate " to be effective 
must neutralize the lime, and also reduce the skin until it 



becomes soft and slippery, and ali^o so act upon the epider- 
mis that the pores are thoroughly opened, so the dirt, 
grease, and fine hairs work out freely upon the beam, leaving 
the skins thoroughly cleansed and in perfect condition for 
tanning, or, I should say, to absorb the n ineral suits to 
which it is subjected. This my " New Solid Bate," which I 
have recently originated, thoroughly aecompli^hes. It has a 
mild fermentive action on the skins and developes in the 
bate vat weak organic acids which neutnilize the lime in a 
perfectly safe way ; it also red uces the skins, opens the pores 
of the epidermis, and thoroughly accomplishes all that is 
required of a bate. 

Its other advantages over dog pure are 

1) It is solid, dry and compact in bulk (100 lbs. to 
cubic foot), but little space is required for storage. Charges 
for transportation are low. 

2) It is all packed in neat 4-lb. paj^er boxes, so marked 
that pounds and half pounds may be cut oft" without bother 
of weighing. 

3) It is clean, and developes no offensive odors, unaf- 
fected by thunder-showers or other atmospheric changes. 

4) It quickly desolves in water, does not require watch- 
ing while in use, as its action is regular and always the 
same. 

5) It contains all the operative and useful properties 
of the old bate, but is free from odor and injurious use- 
less ingredients, such as sand, dirt, etc., which constitute 
about nine-tenths of all dog pure. One case (100 lbs.) 
of new Solid Bate does the work of 75 bushels of dog pure. 



9 

DIRECTIONS FOR USE. 
1 lb. of New Solid Bate is sufficient for 20 dozen skins. 

1) Take a clean barrel, remove the Lead and place a 
spigot in the side about fjix inches from the bottom. 
Place the barrel in convenient proximity to bate vats. 

2) From the package shave with a knife the desired 
quantity into a bucketful of warm water. Rub these shav- 
ings under water between the thumb and finger until dis- 
solved (it will not injure the hands in any way). 

3) Pour this into the barrel which has been filled about 
half -full of warm water, stir well and allow to stand at 
least twenty-four hours. 

4) Draw off nearly all the contents of barrel and pour 
into the warm water of the abating vat, stir well, and put 
in skins, which have been washed after unhairing. 

5) Prepare more bate as before, for the next day, and 
so on. 

6) When the hides are removed from the abating vat, 
run off nearly but not quite all of the old bate liquor. 

It will be noticed that no change in the usual factory 
arrangements are required in using my "New Solid Bate." 
All bates work best in pools or tubs in which there is a 
wheel. Many puresmen do not run off the liquor from the 
abating vat but freshen it up from day to day with new 
bate. If this method is pursued, the contents of the abat- 
ing vat should be well stirred up and about one-third 
drawn oft' every day and warm water and fresh bate solu- 
tion added. In this manner the same bating solution can 
be used for several weeks. 

Price of " New Solid Bate,'' 40 cts. a pound, all packed 
in 4-lb. paper boxes ; 25 of these in 100-lb. cases. One 
4-lb. package free by express, $1.50. 



10 

For skins which are to be alum tanned, the bating 
process is omitted altogether. 

After the skins come from the bate and have been 
worked on the beam, they are then placed "in a 

BRAN DRENCH. 

About 30 lbs. of bran is taken for 20 dozen skins. The 
bran covered with water, allowed to ferment, and the skins 
placed in this. In Germany they rely on bran exclusively 
to remove lime from the skins and properly prepare them 
for the tan. Also manufacturers of straight alum tanned 
stock in this country. The action of the drench is to still 
further " bring down " a skin, and remove the last traces 
of lime. Skins are sometimes " run " in the drench, but 
this happens very seldom. It is important during the 
warm weather to obtain bran free from all adhering parti- 
cles of flour, because bran, when it ferments, produces 
lactic acid which produces the desired result, while flour 
when it ferments produces butyric acid, which is apt to 
injure the stock. For skins to be subsequently tanned 
with chromates the bran drench is emitted altogether. 
After coming from the drench and being washed, the skins 
are now ready for the lanning process. We will first con- 
sider 



11 

ALUM TANNAGE. 

The skins are tanned in a drum with a paste. This 
paste consists of alum, salt, flour and egg yolk, and some- 
times oils of various kinds, as well as sulphur and other 
materials. 

Alum is a double salt (sulphate of aluminia and sul- 
phate of potash) and is but sparingly soluble in water ; 1 
part of alum to 18 parts of water. Skins have a very 
strong affinity for alum, so much so, that a .skin will extract 
from the water the last traces of it. Now as the sulphate 
of aluminia in the alum aloue tans, the sulphate of potash 
being of no value, it would seem that sulphate of aluminia, 
which cau be obtained for about the same price as alum, 
taking into consideration its stronger tanning powei s, would 
be better to use in the tanning mixtures than alum. This 
is no doubt the case, and many manufacturers are using 
sulphate of aluminia in preference to alum. It possesses 
the practical advantage of being much more soluble than 
alum and also makes stock softer. 

Acetate of Aluminia is used in France instead of alum, 
although to my knowledge it is not used at all in this country. 
It has the disadvantage of being more expensive than 
either alum or sulphate of aluminia. It does not separate 
in the skin, it is claimed, in a crystalline form, and the 
leather never becomes spotted. The skins which are tanned 
with the Acetate of Aluminia, ai-e much more solid than 
when tanned with alum. I think this substance is well 
worthy of trial. 

Salt. — The effect of salt is peculiar. It does not seem to 
enter into combination with the skin, but its presence is very 
necessary. Skins tanned without salt are very hard. The 
function of salt no doubt, is to increase the diffusion of 



13 

the alum solution and to precipitate the coriin which pre- 
vents it from gluinfj^ the fibres into a hard mass when it 
dries. In tanning mixtures about half as much salt is 
used as alum. 

Flour is used in the tanning mixtures to attain a cer- 
tain fullness and plumpness. It is the gluten in the flour 
which accomplishes this result — as it has been ascertained 
that the finished skins contain no starch. There is a waste 
product called " Grluten Meal," which contains a much 
larger proportion of gluten than wheat flour does, and 
which costs considerably less. No doubt its merits will soon 
be called to the attention of the trade. In tanning mix- 
tures use about three times as much flour as alum. 

Egg Yolk. — It has been found that Egg Yolk has 
a remarkable softening effect on leather, and it is largely 
used for this purpose, notwithstanding it being so costly. 

Egg Yolk contains water, 52 per cent. ; fat, 30 per 
cent. ; vitelline, 16 per cent. ; inorganic salts, 1.5 per cent. ; 
cholesterm, 0.42 per cent. 

In fact it is a dense emulsion of od suspended in water. 
Vitelline consists of 25 per cent, of albumen, and 75 per 
cent, of fats, also 1 per cent, of sulphur. Three-fourths 
of the fats present are oleine and margarine. Cholesterin 
is contained in small quantities in various parts of the 
animal system, as tlie bile, brain, nerves and blood. 

Now certainly the water and albumen are of no value, 
and the fats present or " Oil of Egg " have no particular 
virtue. The value of egg yolk consists, not in any special 
constitution of the oil, but on account of the fats being so 
finely divided. 



13 

In order to obtain the best results, the Egg Yolks 
should be fresh and not stale. The use of the so-called 
barreled Egg Yolk, which is full of salt, water, and other 
adulterations is not recommendefl. In this connection, I 
would call your attention to my " Egg Yolk Substitute," 
which is compounded in accordance with the results of the 
above recent and accurate analysis of Egg Yolk. This 
preparation is used in the tanning mixtures in exactly the 
same manner and same proportions as Egg Yolk, and has 
a wonderful softening efEect upon leather. Price, 10 cents 
a ft ; put up in 5, 10 and 20 gallon kegs, and by the barrel. 

This preparation may also be used as a fat liquor, by 
mixing it with from 7 to 8 times its bulk of water. 

The above four ingredients are all that is necessary to 
use, to obtain the best results. Some manufacturers, 
however, use oil in their tanning mixtures, to gain as they 
suppose, additional softness and to save egg yolk. Where 
oil is used, it should be most thoroughly in<"orporated with 
the other ingredients. This is accomplished by first mixing 
thoroughly the e^g yolk and flour together with a little 
water and then adding the oil drop by drop, mixing and 
stirring thoroughly all the time. Then add the alum and 
salt, which have been previously dissolved in water, slowly 
stirring and mixing all the time. Lastly, dilute with water 
to the proper consistency. 

Sulphur. — Some parties use this substance in their 
tanning mixtures. They maintain it imparts an additional 
softness to their leather, and assists in "fastening" the tan- 
nage in the stock. This last it undoubtedly does to a small 
extent. It has this undesirable effect, however, it so clogs 
up the pores of the skins, that they require about twice as 



u 

much drumming to get the tanning paste in the stock 
when it contains sulphur. 

After the skins have been drummed with the above 
described tanning mixture for a hour or so, till it is thor- 
oughly absorbed, they are taken out, hung on hooks, and 
dried out as soon as possible. Heat should be used to 
assist the drying process as an alum-tanned skin must be 
dried out quickly to produce the best results. When the 
skins are dried out they should be laid away for some time, 
from 4 to 6 mouths. This " sets the tannage " and softens 
the stock. For if the skins are brought at once to the 
coloring table some of the tannage will be washed out. If 
it is desired to proceed at once to finish the skins, some 
process must be employed to "set the tannage," that is to 
so act upon the tannage that it will be insoluble in water 
and so not be washed out on the coloring table. The 
tannage, where either Alum or Sulphate of Alumiuia is used, 
is Sulphate of Alumiuia, as the Sulphate of Potash in the 
alum has no tanning properties. Sulphate of Alumiuia 
is Oxide of Alumiuia combined with Sulphuric Acid 
(Al2(SOj3. In order to set this tannage it will be neces- 
ary to bring into contact with the Sulphate of Aluminia 
some substance which has a stronger aflSnity for Sulphuric 
Acid than Oxide of Aluminia has, and so take away the 
Sulphuric Acid from the Oxide of Aluminia and leave only 
Oxide of Aluminia in the skin which is insoluble in water. 
The term affinity or chemical affinity is used to describe 
that particular power or force, in virtue of which, union, 
often of a very intimate and permanent nature takes place 
between two or more bodies in such a way as to give rise 
to a new substance. It is a general law that bodies most 
opposed to each other in chemical properties have the 



15 

strongest affinity for each other and evince the greatest 
tendency to enter into combination. Acids are drawn 
towards alkalies and alkalies towards acids, while union 
among themselves rarely if ever takes place. It will be 
seen from the above, as Sulphuric Acid is a very strong 
acid that bringing an alkali in contact with the Sulphate 
of Alumiuia will remove the Sulphuric Acid and accomplish 
the desired result. But it will not do to use too strong an 
alkali such as potash or soda, as the strong alkalies would 
combine with the oil of the egg yolk and remove it from 
the skin. Now when the tannage has been set, either by 
letting the stock lay away, or in the manner indicated 
above, and they have been shaved they are ready to be 
brought to the coloring table. There is one point omitted, 
however, the backs or flesh side of the skins are colored 
either yellow or blue. The yellow color is produced by 
di'umming the skins for a short time with a decoction of 
gambia, fustic or quercitron bark. The blue color is made 
by the use of anilines or logwood. Suitable anilines for 
this purpose can be procured from dealers in aniline colors. 

When the skins are on the coloring table they are first 
subjected to an application of stale urine ; this cuts the 
grease from surface of skins and also acts as a mordant. 
This primitive method is still pursued, but the use of this 
disgusting and offensive material is quite unnecessary. 

My "New Clean Sig" is a perfect substitute. This 
preparation is a clean, dry powder ; keeps perfectly when 
stored, and is always ready for immediate use. It is 
designed to render unnecessary the use of the usual sig in 
tanneries, often difficult to procure in sufficient quantities, 
and always very oft'ensive. It works well, cleans the 
surface of the skins perfectly, also acts as a mordant, and 



16 

gives a thorough preparation for logwood or other mor- 
dants and black. It gives great satisfaction to manu- 
facturers of Dongola and alum-tanned leather, which some- 
times is so hard to color. 

DIRECTIONS. 

Dissolve the powder in warm water and .ipplv in the 
usual way. The strength must depend somewhat upon 
the character of the stock, ^se from 2| to 3 oz. to the 
gallon, according to the character of the stock, its greasi- 
ness, &c. 

Price — 25 cts. a lb. All packed in pails holding from 
25 to 30 lbs. No chai-ge for package. Sample 5 lbs. sent 
prepaid to any address for $1.50. 

For Alum and Chromate stock order white " Sig," 
other tannages, yellow " Sig." 

Next the skins are treated to a decoction of logwood, 
prepared by boiling logwood chips in water. It is best to 
use nothing but water to boil these logwood chips. Some 
add soda or a little urine, but this is apt to produce not 
such a clear and satisfactory black. Fustic chips may be 
boiled with the logwood to advantage. Next a black or 
"striker" is applied and the quality of this is of the 
greatest importance. While a black made from pure cider 
vinegar and iron gives the best results on sumac stock, 
this kind of a black is not suitable for glazed kid. The 
black should form with logwood a deep prussian blue-black 
color and be free from any harshness and any tendency to 
make the grain tender. 

My Standard Iron Liquor Black which is expressly 
prepared for this purpose, gives the very best results and 
although it has been on the market, but a short time is 



17 

used by many of the leading manufacturei's of glazed kid 
in the country. It is free from vinegar and contains no 
copperas, blue stone or anything of that kind. It is care- 
fully manufactured from the best materials by exact rule, 
and tested before sending out, so absolute uniformity may 
be secured. In fact the trade may rely upon each barrel 
being exactly like all others. It is a soft black, sets well 
and quickly, does not strike through, the color is deep 
Prussian blue-black, strong and lasting, will take a bright 
polish or glaze, and remain soft while stored. 



18 

- DIRECTIONS. 

For a " striker " dilute ^ with water and use in the 
ordinary way, without any additions. But one grade is 
made, double strength. Sold by the barrel, 15 cts. per 
gallon net. 

After the application of the striker, the skins are at 
once washed off with water, dried, staked, and some " Sea- 
soning" rubbed on the surface of black, which is allowed 
to dry in. 

Seasonings are prepared in various ways. Some albu- 
minous substance is generally taken, such as Egg White, 
Blood, Milk, &c., and mixed with logwood " black," 
glycerine, gums of various kinds, soap, starch, dextrine, 
gelatine, alcohol, ammonia water, and various other sub- 
stances. Berben-y wine is also used as a " Seasoning." 
It is well in preparing these " Seasonings " to remember 
that it is not well to coagulate the albumen used. Egg 
White is the most sensitive in this respect, and when it is 
heated or any acid brought in contract with it or alcohol, 
it becomes coagulated and the quality of the " Seasoning " 
much impared. I manufacture " Seasonings " suitable 
for the various tannages, to order. 

After the skin is dried, the skins are placed under the 
glazing machine, and when the gloss has been brought up, 
removed, and lastly oiled off. This "oiling off" is to 
convert the prussian blue body black to a jet black. But 
oil applied to an alum skin at this stage, is not at all bene- 
ficial, in fact injurious. I have therefore prepared a black 
which is applied in the usual way, which at once gives a 
rich jet black, and requires no oiling off. This I call 
Glace Black, price 50 cents a gallon. 



19 

CHROME TANNAGE. 

We are indel'ted for this taunajjfe, to several G-erman 
chemists and investigators, Heiuzerling, Caveliu, Vander- 
straaten and others ; to workmen from Germany, who have 
brought valuable secrets with them, and to a Mr. Schultz 
who has a patented process for tanning, by means of 
Chromates. It has long been known that the Salts of 
Chromium have a strong affinity for Gelatine, and there- 
fore tanning poAver. But it is not until very recently that 
this tannage has been made a commercial success. 

All the Salts of Chromium are effective as well as 
Bichromate of Pt)tash, or Magnesia and Chromate of 
Ammonium, Aluminum and Iron. 

But so far manufacturers have confined their attention 
to Bichromate of Potash. 

The skins after being prepai'ed as previously indicated 
are thrown into a drum with bichromate of potash, dis- 
solved in water, and a little muriatic acid. Schultz directs 
for 100 lbs. of skins, 4 lbs. of bichromate of potash, and 
1 lb of muriatic acid. 

The muriatic acid is used for the purpose of plumping 
the skins, and also serves somewhat the same function as 
salt does to an alum tannage. That is, it increases the 
diffusion of the bichromate solution, and also precipitates 
coriin in the skins, preventing it from gluing the fibres 
together into a hard mass. After the skins hare been 
drummed in the above mixture with a suitable amount of 
water for about an hour, it will be found that the tan has 
struck through the skins and they have absorbed pretty 
much all the bichromate; they are then taken from the 
drum. The next process is to set the tannage. The tan- 
nage in this case is Bichromate of Potash K^Cr^O. that is 



20 

Oxide of Potash K^O combined with Chromic Acid Cr^Og- 
Now to " fix" this tannage, it is necessary to convert this 
Chromic Acid Cr.^Og to Chromic Oxide Grfi^. In order to 
do this it will be necessary to bring in contact with it some 
substance which has a strong affinity for Oxygen (0), and 
take away three parts of the Oxygen (0), thus changing 
Cr^Og (Chromic Acid) to Cr.^Oj (Chromic Oxide). 

This is accomplished by Sulphurous Acid (SOJ evolved 
from Hyposulphite of Soda (Na^S.^O.,) by Muriatic Acid 
(HCl) which forms part of Schultz' process ; or by Sul- 
phuretted Hydrogen Gas (H^S), a process which I origin- 
ated ; or by the use of Chloride of Barium, Acetate of 
Lead, Soayj Solutions, Gelatin, and various other methods. 

With the exception of the first two mentioned methods 
the substances named merely set the tannage on the surface 
of the stock. This will not do. Every particle of the 
Chromic Acid pi'esent must be reduced to Chromic Oxide 
or the stock will be hard after drying out from the fat 
liquor. 

For 100 lbs. of skins which have been treated with 4 
lbs. of Bichromate of Potash and 1 ft of Muriatic Acid, 
Schultz prescribes 10 lbs. of Hyposulphite of Soda, and 
2| lbs. of Muriatic Acid. The Hypo, is dissolved in a 
suitable amount of water and the acid slowly added, when 
the following change takes place : 

Na^S^Og (HyposTilphate of Soda) + HCl (Muriatic 
Acid) = SO, (Sulphurous Acid) -f S (Sulphur) + Na,0 
(Oxide of Soda) + HCl (Muriatic Acid). 

Thus we have Sulphurous Acid which is given off as a 
gas with its peculiar characteristic pungent odor. Sulphur 
which separates out as a yellowish white powder and Oxide 
of Soda, which remains in solution as well as Muriatic 
Acid. 



21 

When the Bichromate tanned skins are added to this 
the Sulphurous Acid takes away the excess of oxygen from 
the chromic acid, leaving chromic oxide in the skins and 
forming Sulphuric Acid. In this manner K^Cr.^O^ (Bichro- 
mate of Potash) + SOj (Sulphurous Acid) = K.^Cr.^Oj 
(Oxide of Potassium and Chromium) -f H^SO^ (Sul- 
phuric Acid.) 

The sulphurous acid does its work most thoroughly and 
finished stock, which has been worked with this method, 
may be placed for some tiuie in boiling water without 
extracting any of the tannage. But the process is open to 
serious objections. By setting the tannage in this manner 
not only are the skins subjected to the action of sulphur- 
ous acid, but they are also brought into contact with Sul- 
phuric Acid and Oxide of Soda, as has been explained above, 
as well as to Muriatic Acid. Now the action of these sub- 
stances is injurious, and no doubt accounts for " cracking " 
and other undesirable features. 

Setting the tannage by means of " Sulphuretted Hyd- 
rogen G-as " (Caveat filed). The skins are tanned in the 
same manner as stated above by using 4 lbs. Bichromate 
of Potash and 1 lb. of Muriatic Acid to each hundred 
weight of skins. Then in any suitable apparatus for the 
development of Sulphuretted Hydrogen Gas, Sulphide of 
Iron and water are placed and a little Sulphuric Acid. 
The Sulphuretted Hydrogen G-as (H,S) will at once be 
given forth, it is led by means of a glass tube through 
water to cleanse it from all impurities and finally into some 
vat, tub or other convenient receptacle about half full of 
water in which the skins are placed. The Sulphuretted 
Hydrogen Gas will at once act upon the Chromic Acid and 
reduce it to Chromic Oxide in this manner : 



22 

K,,Cr,0- (Bichromate of Potash) + 4 H,S (Sul- 
phuretted Hydrogen Gas) = K^Cr^O^ (Oxide of Potas- 
sium and Chromium) + 4S (Sulphur) 4- 4 H^O (Water) 
Here we have no superfluous acids liberated to crack the 
grain of the stock, only Sulphur and water which are quite 
harmless. 

But there is some difficulty in working this process 
which will have to be overcome before it will be of j^racti. 
cable value. Sulphuretted Hydrogen G-as is but sparingly 
soluble in water. One part of water will only hold in 
solution 1 part of Sulphuretted Hydrogen Gas while 
it holds 50 parts of Sulphurous Acid. The practical effect 
of this is that in the case of Sulphurous acid the water 
holds such large quantities in solution that it quickly pen- 
etrates to all portions of the skins and accomplishes its 
work, while in the other case much Sulphuretted Hydrogen 
Gas escapes into the air without doing its work and causes 
what to some is a very offensive odor. This difficulty i. e. 
the limited solubility of the Sulphuretted Hydrogen Gas, 
will hare to be overcome before this process is practicable. 

After the tannage is set the skins should be removed 
and at once thoroughly washed to free them from acids 
and then " fat liquored." 

This process of fat liquoring and preparing the fat 
liquor is most important and does not receive the atten- 
tion, as a rule, that is requisite to produce the best results. 

The best " fat liquor " is the oil which is Avorked out 
of skins prepared for glove leather, and I am informed 
that some parties have gone to the trouble and expense of 
soaking damaged, and refuse skins in oil, and then work- 
ing the oil out again. But the usual method is to " cut" 
some oil, say neatsfoot, sperm, or olive, with a little soda, 



23 

and mixing it with eight to ten times its bulk of water. 
In order to make the best fat liquor, the oil should be in 
as fine a state of subdivision as possible'. My " Egg Yolk 
Substitute " is strongly recommended for this purpose, it 
has a remarkably softening effect upon leather. 

The skins are taken from the fat liquor immediately to 
the coloring table before they are dried out and blacked in 
the same manner as has been previously described for 
alum-tanned stock. They ai'e then colored blue, if desired, 
on the flesh side by means of anilines or logwood and hung 
up to dry. When dry they are taken from the hooks, 
shaved, staked and finished in the same manner as alum 
tanned stock. 

The materials which may be used to tan leather for 
glazed kid are endless in number. The Ferric Salts of 
Iron have strong tanning proj^erties and no doubt some 
method which utilizes these materials will be the next 
process used by the trade. 

PRICE LIST. 

I would state for the benefit of those who have never 
dealt with me before, that I guarantee all my preparations 
to be exactly as represented, in so far, that should there be 
any complaint, I will refill the order gratis or refund the 
money paid. The prompt shipment and safe arrival of 
goods is also guaranteed. 

" New Solid Bate," substitute for dog pure, cheaper 
and more cleanly. 1 lb. abates 20 dozen skins. Packed in 
4 lb. paper boxes, 25 of these in 100 lb. cases. Price, 
40 cts. a lb. 

"Egg Yolk Substitute," a perfect substitute for the 
yolk of egg. Price, 10 cts. a lb. Sold by the barrel and 
in 5, 10 and 20 gallon kegs. 



24 

" New Clean Sig," in form a dry powder, 2^ to 3 oz. 
dissolved in a gallon of water, is the proper strength to use. 
Price, 25 cts. Packed in 5, 10 and 20 gallon kegs and in 
barrels. For alum and chromate tanned stock order 
white " Sig," other tannages, yellow " Sig." 

" Standard Iron Liquor" (Black) used either as a tray 
black or striker. Double the strength of vinegar black, 
15 cts a gallon, packed in barrels. 

" Glace Black " has the good qualities of " Standard 
Iron Liquor," with the additional virtue that it requires 
no " oiling off." Price, 50 cts. a gallon. 

PBEPABATIONS FOR BRUSH KID, PEBBLES 
AND SUMAC STOCK. 

" Bleaching Tan Sweetener " keeps tan liquors at all 
times p(;rfectly sweet, makes stock a better and lighter 
color. 2 quarts sufficient for a vat at the start and a small 
quantity every other day, about a pint. Sold by the barrel, 
25 cts. a gallon. 

" E-ussia Stuffing " for oil pebbles, a beautiful, clean, 
pure oil, entirely free from gum and other adulterations. 
Sold by the barrel, 12 cts. a pound. Samples of any of my 
preparations free, recipient to pay expiess charges. 

Address all communications to 

WILLIAM M. NOREIS. 

Princeton, N. J. 

^g^ Beware of worthless and fraudulent imitations of 
my goods. 



LIBRARY OF CONGRESS 

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